Metallothioneins (MTs) are heat-stable low molecular weight proteins characterized by their affinity for metals and high cysteine content. First identified as cadmium-binding proteins (Hamer, D. H. (1986) Annu. Rev. Biochem. 55: 913-952), MTs form high affinity complexes with a variety of trace metals including mercury, iron, platinum, cadmium, and silver, as well as biologically essential metals like zinc and copper. In many cells, MTs represent the single most abundant protein thiol source and the major zinc-binding protein. They regulate intercellular metal concentrations by binding, sequestering, and releasing monovalent and divalent metal ions. MTs participate in zinc and copper homeostasis, regulate the synthesis and activity of zinc metalloproteins, most notably zinc-dependent transcription factors, chelate harmful heavy metals, and scavenge various radicals and reactive oxygen intermediates (Karin, M. (1985) Cell 41:9-10).
MTs have been shown to be efficient free radical scavengers that can sequester reactive metals and inactivate hydroxyl radicals and superoxides. This activity is critical during the acute phase of inflammation where there is a massive release of various species of oxygen metabolites which may be responsible for the initiation of apoptosis. Additionally, MTs are necessary for maintaining the steady-state level of zinc and controlling redox potentials in glutamatergic neurons that sequester zinc in their synaptic vesicles. The concentration of zinc has been shown to be altered in a number of disorders of the central nervous system. Several of these disorders, such as amyotrophic lateral sclerosis, are also associated with oxidative stress suggesting that the induction of MT may provide protection from oxidative damage (Ebadi, M. et al. (1995) Neurochem. Int. 27:1-22; Thornalley, P. J. and Vasak, M. (1985) Biochim. Biophys. Acta 827:36-44).
The intracellular level of MT may play an important role in regulating the cellular responsiveness to DNA interactive antineoplastic agents. Cells with acquired resistance to cisplatin or chlorambucil overexpress MT which binds and sequesters these alkylating agents. In addition to sequestering electrophilic anti-cancer drugs, MTS may alter the therapeutic efficacy of antineoplastic agents by regulating the activities of zinc-requiring metalloenzymes and scavenging radical species (Ebadi, M. and Iversen, P. L. (1994) Gen. Pharmacol. 25: 1297-1310).
Treatment of animals or cells with zinc, copper, cadmium, glucocorticoids, or cytokines increases the concentration of MT proteins by activation of transcription factors that recognize sequence elements located in the 5' untranslated region of the MT genes. All the MT promoters contain multiple copies of these semiconserved sequence elements, called metal-responsive elements (MREs). MREs are 12 to 15 base pair sequences consisting of a highly conserved heptanucleotide core, TGC(A/G)CNC, and less conserved flanking nucleotides. Transcriptional initiation of MT is regulated by a variety of cis- and trans-acting factors that interact with these MREs. Tandem MRE sequences have been used in a yeast one hybrid system to isolate M96, a cognate MRE binding protein. This protein specifically interacts with the MRE in a zinc-dependent manner and probably plays a role in the activation of MTS in the presence of metal ions (Inouye, C. et al. (1994) DNA Cell Biol. 13:731-742).
The discovery of a metal response element binding protein and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention and treatment of cancer, tissue damage and inflammation.